What I'm hearing, he's in a position where he wants to maximize his earning potential on the next contract. I think that just the way things turned out, he did that 8 year deal with Boston that's coming to an end on June 30.
He did that deal during the World Cup tournament in 2016 - clearly, his career went up in a big way from the point he signed that. He probably didn't make as much money for how great of a player he's been.